JPS6115102B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is based on the general formula () F(-SO ₂ -CH ₂ -CH ₂ -OH) _o () (where F represents an organic dye molecule residue, n is 1, 2, 3 or 4) using sulfuric acid and/or sulfur trioxide to obtain the general formula () F(-SO ₂ -CH ₂ -CH ₂ -OSO ₃ H) _o ( ) (wherein F and n have the above-mentioned meanings) The present invention relates to an improved method for producing a sulfuric acid half-ester compound represented by the following formula.

The conversion of a compound represented by the general formula () to a compound represented by the general formula () is known per se. Therefore, esterification of the compound represented by the general formula () is described, for example, in German Patent No.
960534 specification page 5 example 6, German patent no.
1154892 Specification Example 1, German Patent No. 938144 Specification Examples 1 to 3, German Patent No. 1179317 Specification Examples 4 and 5, German Patent No. 1215282 Specification Example 3, German Patent No. 1276842 According to Specification Example 2, Specification Example 9 of German Patent Application No. 1544538, or Specification Example 1 of German Patent Application No. 1644663, using a very large excess of sulfuric acid, i.e.
This is carried out using 22 to 150 times the molar amount of 92 to 96% sulfuric acid. However, this large excess of sulfuric acid requires significant dilution during post-treatment of the esterification product represented by the general formula (), making recovery of the sulfuric acid practically impossible. Moreover, the diluted acid, either in its pure form or in its neutralized form, contaminates the waste liquid as soluble sulfate.

Excess sulfuric acid can be treated by adding calcium carbonate to precipitate calcium sulfate, which can be isolated by filtration and processed into dyes. In this processing method there arises the problem of removing the resulting quantity of wet plaster, which in the form of a slurry overcake is unsuitable for other processing, e.g. to make building materials; Must be stored in special storage.

Other examples include German Patent No. 1268756,
No. 1268759, No. 1544482, No. 1248188 and No.
It is known from the specification of No. 1283416 that the compound represented by the general formula () can be converted into the sulfuric acid half ester represented by the general formula () using several times the molar amount of amidosulfonic acid in pyridine. However, in this case, as all or most of the pyridine used reaches the mother liquor, some amount of pyridine can be removed from the mother liquor before this waste liquor reaches the drain, as shown in the examples. must be removed by some method.

In some examples, the pyridine is recovered by distillation after the reaction has taken place. However, close observation reveals that the amount of pyridine recovered is not the entire amount used. A relatively large amount of pyridine is transferred to the waste liquid with this treatment method.

An urgent problem therefore arises which requires an esterification process which avoids the above-mentioned disadvantages and which in fact does not pollute or hardly pollute the environment.

Now, in converting the compound represented by the above general formula () into the sulfuric acid half ester represented by the general formula () using sulfuric acid, the present inventor has discovered that the compound represented by the general formula () and 92% to 100% sulfuric acid , preferably up to about 70% by weight, especially 15 to 65%
sulfuric acid containing sulfur trioxide or sulfur trioxide itself in a 1- to 5-fold equimolar amount (SO ₃
An improved theory has been found which consists in carrying out the reaction with (with respect to the number of moles of) in a machine operating with a kneading action.

Machines operating with a kneading action are mixers which are suitable for mixing, dispersing or homogenizing and which are capable of kneading liquid/solid components together under the influence of strong forces. In this case, kneading (kneading) can be carried out under high pressure in a conventional manner. That is, parts of the machine that move in parallel or in opposition, in particular at different speeds (for example rolls, disks, rollers, closely meshed gears and worms), are used to move the components under high pressure and possibly under the application of shear forces. Mix with each other. Machines having such a kneading action include, in addition to the actual kneading machines and extruders themselves, for example saw blade stirrers (Teisolver), rotor stator mills, taste spageters and roller mills. These machines operate both discontinuously and continuously. This is known as a number of commercially available products. Kneading machines that operate discontinuously are, for example, double tank types, kneaders (e.g. Sigma paddle kneaders), taste sparging kneaders, Banbury taste sparging mixers, and kneading machines that operate continuously. Machines are, for example, kneading extruders, continuous single-screw and multi-screw kneading machines (described in Ullmanns Encyclopadie
der Technischen Chemie, Volume 1 (1951), No.
pp. 725-727;
Technischen Chemie, 4th edition, Volume 2 (1972), pages 23 and 292-299).

The residue F in the general formulas () and () is a dye residue of various dye classes that can be used for dyeing or printing textile materials. This residue F is used in particular for azo dyes, such as mono-, di-, tri- or polyazo dyes, anthraquinone dyes, phthalocyanine dyes, formazan dyes, nitro,
stilbene, oxazine, diosachidine,
Benzoxanthene, benzothioxanthene,
Dye residues of phenazine and xanthene dyes, of indigoid dyes and of aminoquinone dyes. In addition to the customary and known substituents in these dyes, which may be included in the dye residues, the dyes mentioned above may contain groups which render them water-soluble, such as sulfonic acid-
Or it can also have a carboxylic acid group.

F is a sulfo group-containing anthraquinone dye;
Sulfo group-containing or sulfo group-free monoazo dyes, sulfo group-containing or sulfo group-free copper- or -nickel-phthalocyanine dyes, sulfo group-containing monoazo copper complex dyes, sulfo group-containing xanthenium dyes, sulfo group-containing nitro dyes Dyes, sulfo group-containing or -free copper complex formazan dyes, sulfo group-containing disazo dyes, or sulfo group-containing disazo copper-
Residues such as complex dyes are preferred.

The present invention particularly relates to β-
This invention relates to a method for producing an anthraquinone sulfuric acid half ester compound represented by the general formula (a) from an anthraquinone compound having a hydroxyethylsulfonyl group or an alkali or alkaline earth salt thereof according to the method according to the invention described above. be.

In general formulas (a) and (a), R ₁ is a hydrogen atom or a lower alkoxy group, preferably a methoxy or ethoxy group, particularly a methoxy group or a carboxy group, and R ₂ is a hydrogen atom or a lower alkoxy group. , preferably a methoxy or ethoxy group, preferably a methoxy group,
In this case, at least one of the two substituents R ₁ and R ₂ is a hydrogen atom.

The sulfuric acid used in the reaction is concentrated sulfuric acid (96%)
It is preferably used as a so-called monohydrate (100% sulfuric acid) or as fuming sulfuric acid which additionally contains up to about 65% by weight of sulfur trioxide. As an esterifying agent, sulfur trioxide itself is used in an amount of 1.1- to 4-fold relative to the number of moles of SO ₃ and the free acid represented by the general formula ().
Preferably 1.1 to 2.5 times, especially 4.3 to 2.5 times
Preferably, 2.5-fold equimolar amounts are used.

Therefore 96-100% sulfuric acid and SO ₃ - content 70
It is preferred to use up to % by weight of oleum.

The starting compound represented by the general formula () can be used in the form of a free sulfonic acid or in the form of an alkali or alkaline earth salt. Therefore, when a salt is used, more sulfuric acid is required to convert it into an acidic compound than when the compound represented by the general formula () is used in the form of a free acid.

The implementation of this process can be as simple as first adding one of the reactants into the kneader and then gradually adding the other component thereto, or introducing both components simultaneously or as a mixture into the kneader. done in a method.

The reaction temperature can be between +10°C and 200°C. The reaction with sulfuric acid or oleum or sulfur trioxide is carried out in a kneading machine (a machine with a kneading action) for 10 minutes.
It is advantageous to carry out the process at a temperature of from 80° to 170°C, in particular from 80° to 120°C. The processing time of the reaction mixture in the kneading machine varies from a few minutes to several hours, depending on the temperature and kneading intensity. Applied kneading strength −
This, on the other hand, can depend on the type of machine - it is expedient to operate at temperatures of 80 DEG to 120 DEG C. and within a reaction and kneading time of 2 minutes to 2 hours, depending on the type of machine.

During the kneading process, inert additives, such as o-
Additions of dichlorobenzole, diatomaceous earth, talc or metal powders can also take place. This can then be removed again from the produced sulfuric acid half ester of the general formula () during processing of the blend.

The processing of the reaction mixture in the kneader after esterification is carried out in a manner customary and customary to those skilled in the art. This processing is advantageously carried out by dissolving the reaction mixture in water and simultaneously neutralizing the solution.
This neutralization is preferably carried out using sodium bicarbonate or sodium carbonate. The neutral or very weakly acidic dye solution is then evaporated to dryness or spray-dried, optionally after separation of the above-mentioned inert additives, for example after filtering or centrifugation. When neutralized using, for example, the above-mentioned sodium salt in this method, a compound represented by the general formula () is obtained in the form of its (di)sodium salt. Correspondingly, potassium bicarbonate or potassium carbonate can also be used for neutralization. The processing possibilities of other admixtures consist of the following: That is, after dissolving in water and neutralizing with calcium carbonate, the calcium sulfate formed and precipitated is sucked off, then sodium oxalate or oxalic acid and sodium carbonate or bicarbonate are added to the solution and this solution is dissolved. is separated from the precipitate formed in a conventional manner, for example by filtration or centrifugation, and then spray-dried.

Compounds of the general formula () can be prepared by the process according to the invention described above with a degree of esterification of 95-100%. According to the method of the present invention, in addition to the above-mentioned advantages that only a slight excess amount of sulfuric acid is required and thereby contamination of waste liquid or the environment is significantly reduced, the compound represented by the general formula () is additionally used. Surprisingly, it is obtained in a higher quality than the compounds obtained according to known methods. The compound represented by the general formula (), which is important as a dye, has a high degree of esterification, solubility in water, and dyed products or Excellent color purity of printed materials (cellulose fiber materials).

The following examples serve to illustrate the method according to the invention. The relationship between "parts by weight" and "parts by volume" described in the examples is the relationship between "Kg" and "."

Example 1 While the machine is running in a commercially available taste pager kneading machine (for example Buerner & Pfreiterer, Stutsgart Heuerbach),
3.281 parts by weight of sodium 4-(3'-β-hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-2-sulfonate (92%) are first introduced. Then add 100% sulfuric acid 1.042
Add volume over 2 minutes. The initially wet mixture develops a viscosity during kneading - during which time the temperature rises to about 100 DEG C. within 25 minutes. After 40 minutes of adding sulfuric acid, the kneaded material having a temperature of 100-105°C is taken out from the kneading machine.

0.2 parts by weight of the kneaded product is mixed and stirred at 0-5°C into a mixture consisting of 0.6 parts by volume of water and 0.2 parts by weight of ice.
At the same time, approximately 0.109 parts by weight of sodium bicarbonate is successively added. The pH value of the dye solution obtained is
It will be 4.0 or 4.5. The solution is clarified and evaporated to dryness under vacuum at 60-65°C. After grinding, 0.222 parts by weight of a dark blue dye powder are obtained. This is the following formula (A) This corresponds to 64% by weight of the dye (molecular weight 626) expressed by

Example 2 A commercially available Bumperley taste sparging mixer (e.g. Buerner & Pfreiterer, Stutsgart-Heuerbach) - one of its kneading arms has a speed of 29 revolutions per minute and the other arm has a speed of 21 revolutions per minute. Sodium 4-(3'-β-hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-2-sulfonate (92%)
3.138 parts by weight are first introduced at room temperature. within 5 minutes
1.617 parts by weight of 100% sulfuric acid are added and the reaction mixture is kneaded for 25 minutes by means of a hydraulically reduced pressure piston. The mixture reaches a temperature of 125°C.

0.2 parts by weight of the kneaded product are introduced at 0-5 DEG C. into a mixture consisting of 0.6 parts by volume of water and 0.2 parts by weight of ice. By adding 0.06 parts by weight of calcium carbonate, the PH- value was increased.
Adjust to 4.0 or 4.5. The reaction mixture is heated to 70-75° C. by introducing steam and the calcium sulfate formed is then removed. Wash this several times with hot water. Cool the liquid and cleaning solution to approximately 30°C.
To this is added 0.012 parts by weight of oxalic acid at this temperature. PH using approximately 0.016 parts by weight of sodium bicarbonate
−Adjust the value to 4.0 or 4.5. The reaction mixture is approx.
Stir for 30-60 minutes at about 25-27°C to remove the formed precipitate and spray dry the liquid.

0.16 parts by weight of dye powder is thus obtained, which contains 90% by weight of the dye of formula (A) given in Example 1.
corresponds to

Example 3 4-(3'-β-Hydroxyethylsulfonyl-phenyl-amino)-1-amino in a taste pager-kneading machine whose kneading arms operate at speeds of 22 and 16 revolutions per minute. -2.932 parts by weight of sodium anthraquinone-2-sulfonate (92%) are kneaded with 2.11 parts by weight of 100% sulfuric acid for 1 hour. The temperature is then gradually increased to 95-100°C using a jacket heater. After removing the kneading material from the kneading machine, 0.2 parts by weight of the kneading material is worked up as described in Example 2 and spray dried.

0.136 parts by weight of dye powder are thus obtained. This corresponds to 92% by weight of the dye of formula (A) shown in Example 1.

When treated according to the method described in Examples 1-3, the compounds shown in the following table can be converted to their corresponding sulfuric acid half esters.

EXAMPLE 7 1.2 parts by weight of diatomaceous earth is first introduced into a commercially available bumper-taste persion kneading machine, in which one of the kneading arms operates at 31 revolutions/min and the other at 22 revolutions/min; To this is added 2.25 parts by weight of 100% sulfuric acid over a period of 2 to 3 minutes. Then rapidly 4-
(3'-β-hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-2
- 3.2 parts by weight of sodium sulfonate (90%) are introduced. Knead for 100 minutes using a hydraulically low-pressure piston and a jacket heater using hot water. At that time, the internal temperature will be 120-125℃.

0.2 parts by weight of the kneaded product are introduced at 0-5 DEG C. into a mixture consisting of 0.6 parts by volume of water and 0.2 parts by weight of ice. At the same time, the pH value is maintained at 5.8-6.2 by successively adding a total of 0.07 parts by weight of sodium bicarbonate. The resulting blue solution is clarified and spray dried.

0.185 parts by weight of blue dye powder are thus obtained. This corresponds to 54% of the dye of formula (A) shown in Example 1.

Example 8 Commercially available continuous kneading machine (e.g. Buss-KO-kneading machine, model PR46 from Bues AG, Parsel/Switzerland)
- It operates at 26 revolutions per minute - 4- (3'-
41.2 g/min of sodium hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-2-sulfonate (92%) were introduced via a metering worm and then via a metering pump.
Add 11.6 ml/min of 100% sulfuric acid. The kneading machine is maintained at a temperature of 95-100°C by steam. The resulting kneaded material has a density of 1.6-1.7 g/cm ³ .

0.2 parts by weight of the kneaded material produced continuously are worked up according to Example 2.

0.16 parts by weight of dye powder are thus obtained. This corresponds to 90% of the dye represented by formula (A) shown in Example 1.

Example 1a−8a Continuous kneading machine for relatively large insertion amounts (e.g.
Buss AG's or series "Buss-Ko-"
Kneter" Parsel/Switzerland) or twin-screw mixing and kneading extruders (e.g. Buerner &Preiteler's"Continua" kneading extruder or equipment with a main kneading rotation shaft and a cleaning rotation shaft, e.g. H.
Good results similar to those in the above example are obtained using the "AP-Conti-Reaktor" from List (Pratstern/Switzerland).

Example 9 (a) 4-(3'-β-Hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-2-sulfonic acid in a commercial taste pager kneader with heating or cooling jacket. 3493 parts by weight of sodium (90%) (dry powder) are first introduced. Then 370 parts by weight of 65% oleum and 100% oleum were added in one hour in a machine with two kneading arms operating at about 36 or about 28 revolutions per minute.
A mixture consisting of 1060 parts by weight of sulfuric acid is added. This mixture was kneaded for another 30 minutes in the kneading machine and then
100-110 by jacket heater within 30 minutes
Keep at ℃. Next, the mixture is cooled to room temperature using a jacket cooler, and the kneaded product is taken out.

Thus, 4900 parts by weight of red-blue powder was obtained, which corresponds to 70% by weight of the dye represented by the above general formula (a) (R ₁ and R ₂ are hydrogen atoms).

(b) Add 41 parts by weight of the dye powder obtained in (a) to 240 parts by weight of water.
11 parts of soda calcined at 10-20°C in 60 parts by weight of ice
Spread part by weight and dissolve at PH4.5-5.0. The dye solution obtained is clarified and then dried on a drying plate at 50-60° C. in an air circulation drying cabinet or a vacuum drying cabinet. The dried material is then ground.

45 parts by weight of dark blue dye powder are thus obtained. This corresponds to 68% of the dye represented by formula (A) shown in Example 1. It is highly suitable for dyeing or printing cellulose fabrics according to the customary application methods for reactive dyes. A dyeing or print of a very pure blue shade is thus obtained.

Example 10 (a) 4-(3'-β-Hydroxyethylsulfonyl-phenylamino)-1 in a taste pager kneading machine with a heating or cooling jacket.
4020 parts by weight of -amino-anthraquinone-2-sulfonic acid (dry powder) are first introduced. A mixture consisting of 857 parts by weight of 65% oleum and 196 parts by weight of 100% sulfuric acid is then poured within 30 minutes in a machine with two kneading arms operating at about 36 or about 28 revolutions per minute. The reaction mixture is kneaded for an additional 30 minutes and then carefully heated to 90-100°C via a jacket heater. As soon as the powdered mixture has changed into relatively large blocks, switch to the jacket cooler with water and keep the temperature during kneading at 90-100°C for a further 30 minutes. Thereafter, it is cooled to room temperature using a jacket cooler, and the kneaded product is taken out.

A reddish-brown powder is thus obtained, which corresponds to 92% of the dye of the general formula (a) (R ₁ and R ₂ are hydrogen atoms).

(b) Add 634 parts by weight of the reddish brown dye obtained in (a) to water.
Sprinkle 160 parts of calcined soda in 3,000 parts and 500 parts of ice at 10-20°C and dissolve at PH4.5-5.0.
The dye solution obtained is clarified and dried on a drying plate at 50-60° C. in an air circulation drying cabinet. (The ester can also be isolated by vacuum or spray drying.) 730 parts by weight of a dark blue powder are thus obtained, which contains the dyestuff of the formula (A) shown in Example 1.
Corresponds to %.

This dye is a conventional printing dye for reactive dyes.
Alternatively, it can be applied on cotton by dyeing-methods.

(c) Thoroughly grind 63 parts by weight of the dye powder obtained in (a) and 16 parts by weight of calcined soda in a mixer.

79 parts by weight of a reddish-brown powder are thus obtained. This corresponds to 73% of the dye represented by general formula (a) (R ₁ and R ₂ represent hydrogen atoms). This can be applied to cellulose fiber materials according to the printing or dyeing processes used in industry for reactive dyes, giving dyeings or prints of very pure blue tones.

Example 11 Continuous twin-screw kneading extruder (worm diameter 120 mm and effective length approx. 150 cm) - the worm consists of four sections offset in the same direction between the transfer members.
It has two kneading block pairs consisting of two kneading block pairs and four parts positioned in opposite directions, and has a rotation speed of 80 revolutions/min - 4 in.
-(3'-β-hydroxyethylsulfonyl-phenyl-amino)-1-amino-anthraquinone-
127 kg/h of sodium 2-sulfonate (89%) is metered in using a conveyor-type meter. at the same time
73 kg/h of 100% sulfuric acid are added using a metering pump shortly after the introduction of the powder. the first reaction vessel
Heat the next reaction vessel to 8℃ using hot water at 80℃.
Cool with water. Kneaded material (density 1.6-1.7
g/cm ³ ) is 115°C. There are many mixtures
Occurs in cm-sized lumps. In this form it is suitable for further processing in a neutralized aqueous phase. If the blend is passed through a perforated plate and separated into uniform cylindrical shapes by periodically operating cutters, an easily processable and easily transportable product is likewise obtained.

Experimental conditions can be varied over a wide range when using a continuous two-rotating shaft kneading extruder. Thus, for example, the rotational speed can be increased considerably.
Thus, it can be increased, for example, to 250 revolutions/min or reduced to, for example, 50 revolutions/min.
This change does not have a significant effect on very high degrees of esterification. Also, the effective length of the worm can be varied, or the worm installation can be varied in terms of the number and set of transfer members and kneading blocks. Similarly, 4-(3'-β-hydroxyethylsulfonyl-phenyl-amino)-1
-The amount of sodium amino-anthraquinone-2-sulfonate is, for example, 85.3% starting material compound 95Kg/
h and 100% sulfuric acid 55Kg/h can be easily and rapidly changed.

The resulting kneaded product can be processed, for example, by introducing the kneaded product into water, neutralizing it, and then spray drying it in the same manner as described in the previous examples.

Example 12 A commercially available teaspersion-kneading machine (e.g. Buerner & Pfreiterer), in which one kneading arm operates at 28 revolutions/min and the other at 21 revolutions/min - powdered 2-(3'-β-hydroxyethylsulfonylphenyl-azo)-1-hydroxynaphthalene-4-sulfonic acid (79%)
3320 parts by weight are first introduced. Then 100% sulfuric acid
Drop 1470 parts by weight over 10 minutes. The resulting mixture is kneaded for 4 hours at 60-85°C.

80 parts by weight of the obtained kneaded product were introduced into 1050 parts by volume of water, and the pH value was adjusted with sodium bicarbonate at 5-10°C.
Adjust to 4.5-4.8. This mixture is spray dried.

86 parts by weight of dye powder are thus obtained. This is 2-(3′-β-sulfatoethylsulfonylphenyl-azo)-1-hydroxy-naphthalene-4
-Sulfonic acid di-sodium salt (molecular weight 528)
This corresponds to approximately 59%. The dye powder obtained dyes cellulose fibers in yellowish-red tones according to the dyeing methods used for reactive dyes.

Example 13 Taspersion - kneading machine (for example Buerner & Pfreiterer) - its kneading arm is 29
or operating at 21 revolutions/min - in powder form 2-
[2′-(5″-β-hydroxyethylsulfonyl-
2″-Hydroxy-phenyl-azo)-1′-hydroxynaphthalene-6′-azo-(8-amino-1-
3846 parts by weight of a monocopper complex of (hydroxy-naphthalene)-3',5,7-trisulfonic acid (67%) are first introduced. Next, add 750 parts by weight of 100% sulfuric acid to approximately 15 parts by weight.
Drop for 7 minutes and dry thoroughly at 70-80°C for 7 hours.

The resulting kneaded product is neutralized in water in the same manner as in the previous example. The dye is isolated from this solution by evaporative concentration.

A dark blue powder is thus obtained. This dyes cellulose fibers marine blue.

Examples 14-174 The following dyes can be easily prepared with a high degree of esterification from their corresponding β-hydroxyethylsulfonyl compounds by a method analogous to Examples 1-13.

Claims (1)

[Claims] 1 General formula () F(-SO ₂ -CH ₂ -CH ₂ -OH) _o () (wherein, F represents an organic dye molecule residue, and n is 1, 2, 3 or the number of 4) by esterifying a compound represented by the general formula () F( _-SO2 - _CH2 - _CH2 - _OSO3H ) _o () (in the formula , F and n have the above-mentioned meanings), this reaction is carried out using 92% to 100% sulfuric acid, sulfuric acid containing sulfur trioxide, or sulfur trioxide itself to 1- to 100% sulfuric acid. A process for the production of half-ester compounds as described above, characterized in that it is carried out in a machine operating with a kneading action using 5-fold equimolar amounts (relative to the number of moles of SO ₃ ). 2. The method according to claim 1, which is carried out at a temperature of 80 to 120°C. 3. The method according to claim 1 or 2, which is carried out in a continuous single- or multi-screw kneading machine. 4. The method according to any one of claims 1 to 3, which comprises using 96-100% sulfuric acid or sulfuric acid containing sulfur trioxide as the esterifying agent. 5 General formula (a) (In the formula, R ₁ means a hydrogen atom, a lower alkoxy group or a carboxy group, R ₂ means a hydrogen atom or a lower alkoxy group, and in this case, two substituents
At least one of R ₁ and R ₂ is a hydrogen atom. ) or its salt to the general formula (
a) A method according to any one of claims 1 to 4, which comprises producing an aminoanthraquinone compound represented by the following formula: (wherein R ₁ and R ₂ have the meanings given above). 6 In general formulas (a) and (a), R ₁ and
A method according to claim 5, characterized in that R ₂ each represents a hydrogen atom. 7. The method according to claim 5, wherein in the general formulas (a) and (a), R ₁ is a carboxy group and R ₂ is a hydrogen atom. 8. The method according to claim 5, wherein in the general formulas (a) and (a), R ₁ is a hydrogen atom and R ₂ is a methoxy group.